Thermionic vacuum tube



Feb. 25, 1930. w. H. T. HOLDEN 1,748,175

' THERMIONIC VACUUM TUBE Filed Sept. 24, 1925 Hilanuv/Lt (ht/wile hareL'lmuge Electrode 7.9 (ontrol Grid 16 V bk/Pen Grid 1 Plate 22&Evacuated [In 06w? Sate/46nd Plate e 221 15 226 l v /.7

14 [flan/Lent Monk pace Charge Electrode llf lg Gnmtrol Grid :i ESaree/1y Grid I I I II I I II 10 I "l H I I H :{l I I I :t F M 1 :1*-':E17-\ I I 3 INVENTOR ATTORNEY Patented Feb. 25, 1930 UNITED STATES PATENTOFFICE WILLIAM H. '1. HOLDEN, OF BROOKLYN, NEW YORK, ASSTGNOR TOAMERICAN TELE- PHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK'rnnnmromc VACUUM TUBE Application filed September 24, 1925.

This invention relates to vacuum tubes of the electron discharge typeand particularly to a tube of that type characterized by a number ofelectrodes greater than three, the said electrodes being so arrangedthat the impedance of the path between the plate and the filament is notappreciably greater than that of the three-electrode tube.

In the development of the art of high frequency signaling it has beenfound desirable to employ vacuum tubes having more than threeelectrodes, but with the tubes heretofore developed diflicult y has beenexperienced owing to the fact that the plate-filament impedance has beenmaterially increased due to the separation of those electrodes, whichhas been rendered necessary by the insertion of additional electrodesbetween them.

My invention resides in a vacuum tube having more than three electrodes,characterized by an electrode in the same plane as the filament, whichelectrode may be used as a space charge electrode or as a controlelectrode.

This invention will be clearly understood from the following descriptionwhen read in connection with the attached drawing, of which Figure 1 isa horizontal cross-section through a tube having a space chargeelectrode lying in the same plane as the filament and having two gridslying between the filament and the plate of the tube; Fig. 2 (also across-sectional view) shows a simpler form of tube having a single gridbetween the filament and the plate, and Fig. 3 shows diagrammaticallythe arrangement of the various electrodes of a tube of the type shown incross-section in Fig. 1.

In Figs. 1 and 3, in which the same numerals have been used to representthe same parts, the plate 10, which has been shown as being broken awayin order to disclose the inner electrodes, is supported by means of therods 11 and 12 which are embedded in the stem of the tube. The rod 11 isconnected with the conductor 6, by means of which the plate may beconnected with the circuit in which it is to be used. The member 13 isconnected with the upper edge of the plate in order to support one endof the member 15 which serves to support the other elec- Serial No.58,397.

trodes of the tube, and also serves to keep the electrodes properlyspaced apart. The other end of this member 15 is supported by the member1a which would be connected with the upper edge of the plate which hasbeen shown as broken away. Immediately adjacent the plate, and betweenthe plate and the filament, is the screen grid 16, which is supported bymembers connected with the member 15, and is also supported by the stemthrough the rods 17 and 18, the latter being connected with theconductor 5 for the purpose of connecting this electrode with theexternal circuit. Between the screen grid and the filament is a controlgrid 19, which in construction resembles the screen grid 16. The grid 19is supported in part by the member 15 and also by the rods 20 and 21which are embedded in the stem of the tube. The rod 20 is connected withthe conductor at in order to connect this electrode with the externalcircuit. \Vithin the control grid 19 are two electrodes, namely, thespace-charge electrode represented in three parts designated 22, and22*, and the filament 26. As will be seen clearly in Fig. 1, thespacecharge electrode and the filament lie in the same plane, whichmethod of construction reduces the space between the filament and theplate and thereby serves to keep down the impedance of that path. Theparts of the space-charge electrode are conductively connected bylinking members, as shown in Fig. 3 at the upper ends of these parts,and the lowerparts are connected by means of the rods 23,24: and 25 withthe stem of the tube, thereby adequately supporting the various parts ofthis electrode. The rod 25 is connected with the conductor 3 in order toconnect this electrode with the external circuit. The filament 26 issupported in part by the member 15, and also by the rods 27 and 28,which are imbedded in the stem and-are connected, respectively, with theconductors 1 and 2.

In order to clearly understand the nature of this invention it may bedesirable to define certain terms heretofore used. A spacechargeelectrode is defined as an electrode near the cathode, to which apositive potential is applied in order to reduce the efl'ect of the neative space charge of the electrons emitted from the filament or thecathode. The use of a space charge electrode reduces the plate impedanceof the tube and permits operation at lower plate voltages than otherwisewould be feasible.

The control electrode, which may be defined as the electrode to whichthe input voltage of the circuit is applied, is illustrated by the gridof the well-known threc-clectrode tube.

A screen grid is defined as a grid between the plate and the controlelectrode to which is applied a positive potential less than, equal to,or greater than the plate potential. This electrode serves to screen theinput or control electrode from the plate. and to greatly reduce thetcndcncv to feed back from the plate to the control grid through thecapacity of the .vacuum tube elements while at the same time thearrangement shown in Fig. 2 is a simpli-' tied form of the tube shown inFig. "1. In a tube of the type shown in Fig.2 an electrode co-planarwith a filament could be utilized as the control electrode of the tube,and the grid between the filament and the plate could be utilized as thescreen grid. It will of course be obvious that if two electrodes areplaced in the same plane, the necessary distance from the cathode to theanode in a vacuum tube of the multi-electrode type may be reduced ascompared with the distance required if the various electrodes lie indifierent planes, provided of course that in both cases embodied inparticular forms and arrangements of parts, it is to be understood thatit is capable of embodiment in other and different forms withoutdeparting from spirit and scope of the appended claims.

What is claimed is: 1. A vacuum tube comprising an evacuated theenvelope enclosing a cathode for the emission of electrons, an anode, agrid interspaced between the said cathode and the said anode to controlthe flow of electrons between the latter electrodes, and a space chargeelectrode co-planar with the said cathode.

2. A. vacuum tube comprising an evacuated envelope enclosing a. cathodefor the emisslon of electrons, an anode surrounding the said cathode, aid also surrounding the said cathode an interspaced between the saidanode and the said cathode, and a space charge electrode co-planar withthe said cathode.

3. A vacuum tube comprising an evacuated envelope enclosing a cathodefor the emission of electrons, an anode surrounding the said cathode, ascreen grid also surrounding the said cathode and interspaced betweenthe said anode and the said cathode, a control'grid surrounding the saidcathode and interspaced between the said screen grid and the saidcathode, and a space charge electrode co-planar with the said cathode.

In testimony whereof, I have signed my name to this specification this22nd day of September, 1925.

- WVILLIAM H. T. HOLDEN.

. the clearances between successive electrodes

